The present invention relates to a rotary actuator having a permanently magnetized rotor and a plurality of stator windings surrounding the rotor in a rim-like fashion, for generating magnetic fields that place the rotor in one of a first plurality of positions.
Rotary actuators can be used as the drive for rotary switches, for example, an xe2x80x9cRxe2x80x9d-type waveguide switch in satellite technology.
Currently, stepping motors are generally used as actuators for purposes of this type, such as are described in European Patent No. 0 635 929. However, stepping motors have a number of characteristics that make them not seem optimally suited as actuators for rotary switches. Stepping motors are generally designed to generate a large torque that is distributed as uniformly as possible in the course of one rotation of the motor shaft, the torque making it possible to smoothly drive a mechanism that is braked using friction. This requires a minute staggering of the stator windings in the circumferential direction around the rotor, necessitating a multiplicity of terminal connections that are cumbersome to connect to wires. FIG. 5a depicts an example of a rim-like arrangement of stator windings, which can place an (undepicted) rotor in four positions, each offset by 45xc2x0 with respect to the others. Stator windings 1 through 4 are divided here into two diametrically opposite segments 1a, 1b, . . . 4a, 4b. The total of eight segments are mounted on a ring core 5, which lies in the plane of the Figure and perpendicular to rotational axis 6 of an (undepicted) rotor. FIG. 5b depicts the alignments of magnetic fields B1 . . . B4, which are obtained by sending current through segment pairs 1a, 1b . . . 4a, 4b. These vectors indicate the position in which the rotor is placed in the interior space of ring core 5. Each neighboring vector has an angular distance from adjacent vectors of 45xc2x0. By sending current through the winding segments having the opposite sign, vectors can also be generated in the opposite direction, but they generally have no practical significance in applications of the rotary actuator for setting a rotary switch.
The large number of necessary segments makes it difficult to achieve a compact design of the actuator and renders its manufacture time-consuming and expensive.
From Japanese Laid-Open Patent Application No. 10 178 770, and the related English abstract published in Patent Abstracts of Japan, Volume 1998, No. 11, Sep. 30, 1998, a motor, in particular a stepping motor, is known which has a controllable stop position. This motor has a permanently magnetized rotor and a plurality of stator windings surrounding the rotor in a rim-like fashion, for generating magnetic fields for the purpose of placing the rotor in a plurality of positions. To place the rotor in specific positions, permanent magnets are provided between the stator windings.
According to the present invention, in a rotary actuator of the type cited above, elements are provided for exerting a corrective torque on the rotor, the elements, in the currentless state of the stator windings, placing the rotor in a target position from a second plurality of positions, a target position being assigned to each position of the first plurality. Therefore, whereas in conventional rotary actuators the stator windings themselves must place the rotor in a target position, in the actuator according to the present invention, this task is taken on by the elements for exerting a corrective torque. Therefore, there no longer exists the requirement that the stator windings must have an arrangement having double symmetry in order to be able to set n different positions in an angular range of 180xc2x0. Their arrangement can therefore be simpler, a high degree of symmetry in any case in the elements for exerting the corrective torque. But since the latter is smaller than the torque to be exerted by the stator windings and since the range of the latter can be significantly smaller, it is possible that the elements for exerting the corrective torque can also be significantly smaller and more compact.
In particular, these elements can be permanent magnets and therefore do not need to be wired. Thus according to the present invention, it is possible to arrange the stator windings about the rotor in an unpaired fashion, which cuts in half the number of contacts that are needed for the power supply of the stator windings, and that must be soldered or connected in some other way. The possibility of using a number of stator windings that is smaller than the number of the first positions makes possible a further simplification of the design.
According to one preferred embodiment, the rotary actuator has four first positions and three stator windings.
Further features of the rotary actuator according to the present invention and of a rotary switch that is equipped with an actuator of this type can be derived from the description of the exemplary embodiments below.